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Practice and understanding of comprehensive supporting technology for adjustment well drilling in Qinghai Oilfield Lu Jingwen Hu Qunai Liu Zhenyu Shi Jianguo Yi Ming Xinhuatugou, Shizigou and Qiquan are the three main blocks for oil and gas development in Qinghai Oilfield. The geological conditions of these blocks are complex. The shallow strata are loose, with developed gravel layers, faults, and cracks. The stratum dip angle changes greatly. The distribution of oil and gas layers is shallow, thin, scattered, and numerous. The formation pressure coefficient is low, only 0.6 to 0.8. During the drilling process, complex situations such as well deviation, well leakage, well collapse, diameter reduction, and stuck drilling are prone to occur. During completion and cementing, the oil, gas, and water layers can easily contaminate the cement slurry, causing the cementing quality to fail to meet requirements. In addition, most of the wells drilled in these blocks are cluster wells, directional wells or small-displacement wells. In 2001, we completed a total of 22 wells in these blocks. Through the implementation of comprehensive supporting technologies for adjustment well drilling, the average ROP of the completed adjustment wells reached 17.24m/h, which was 54% higher than that in 2000 (average ROP 11.20m/h). Among them, Well 76-30 completed a footage of 1180m in 6.54 days, with a ROP of 24.63m/h, setting a record for the block. 1. Geological characteristics of the main blocks of the Qinghai Oilfield. The Huatugou Oilfield is located in the southern part of the western Qaidam Basin. It is the main high point of the Shizigou structure in the Mangya depression of the Shizigou structural belt in the Yousand Mountain anticline. It is the old oil field with the highest altitude, the most difficult conditions and the worst natural environment in China. The stratigraphic layers are mainly the Lower Youshashan Formation (N21) and the Upper Ganchaigou Formation (N1). The lithology is mainly sandstone and mudstone, interbedded with conglomerate, conglomerate sandstone, gravelly mudstone, siltstone and argillaceous siltstone and mudstone. The interbedded layers are of varying thickness and frequently interact. The porosity is 18%~21%, and the permeability is (22~110)×10-3μm2. The current formation pressure coefficient is 0.6~0.8. During the drilling process, well deviation, well leakage, and stuck pipe are relatively serious, and the reservoir is characterized by being thin, numerous, scattered, mixed, and highly heterogeneous. The Shizigou structure is located on a third-level structure on the Shizigou-Yousha Mountain backslope structural belt in the western depression area of the Qaidam Basin. This structure is dominated by fracture reservoirs, with well-developed fractures and high surface gravel content. The reservoir lithology is mainly various impure carbonate rocks, which are pore, dissolved pore and fracture oil storage strata. Complex surface and underground geological conditions make well deviation, leakage, diameter reduction, and drilling jumps more serious during the drilling process. The Qiquan Oilfield has a high content of clay minerals. Drilling data confirms that there are multiple sets of interwell faults at high points in the area, which can easily cause well deviations and shrinkage during drilling. 2. Research and application of drilling supporting technologies. Based on the geological characteristics of the Qinghai Oilfield, relying on the drilling experience accumulated by our company in the internal and external markets over the years, and through repeated and careful research, testing and application in the Qinghai Oilfield site, we have perfected and summarized a systematic set of comprehensive supporting technologies for adjustment well drilling. 2.1 Drilling parameter optimization technology By optimizing drill bits and drilling parameters, and applying fast drilling technology dominated by large drilling pressure, high rotational speed, and enhanced well trajectory monitoring, remarkable results have been achieved. 2.1.1 Drill bit selection Based on the geological characteristics of each block in the Qinghai Oilfield, combined with adjacent well data and years of drilling practice experience, the depth of the φ311.2mm surface adjustment wells constructed in the Huatugou, Shizigou and Qiquan blocks is generally within 200m. The focus was on 8in (215.9mm) drill bits, and the highly economical H517 and HJ517 tricone bits were selected. 2.1.2 Optimization of drilling pressure and rotational speed After testing multiple wells and conducting comprehensive economic comparisons with multiple drilling companies, the highly economical H517 or HJ517 drill bit suitable for this area was selected. Drilling parameters of high drilling pressure (120-200kN) and high rotational speed (90-200r/min) are adopted, high-quality drilling fluid is used to ensure downhole safety, well deviation is strictly monitored, and for wells whose predicted displacement or trajectory exceeds the standard, wires are installed in a timely manner to twist the azimuth while drilling. 2.1.3 Displacement The optimal displacement depends on the specific conditions of the well. Generally speaking, the ROP increases with the increase in displacement, but it must be considered to meet underground safety, prevent leakage, and prevent jamming, and prevent excessive displacement from washing the well wall. Too small displacement will not completely carry sand, causing complexity downhole. Generally speaking, about 28L/s is appropriate for an 8in (215.9mm) wellbore. 2.1.4 Specific water power of the drill bit In order to improve the specific water power of the drill bit, oblique nozzles and medium-long nozzles are used, a suitable well section is selected to make full use of good pump conditions, and high-pressure injection is carried out. According to statistics, the use of special nozzles can increase the mechanical penetration rate by 30% to 40%. Only in the 12 completed wells in the Huatugou block, a total of 28 roller drill bits were consumed, the nozzles were used 76 times, and the special nozzles were used 54 times. The special nozzle usage rate was 71.05%. Compared with the previous wells using special nozzles in the same block and the same depth, the footage of a single drill bit increased by about 4%, and the mechanical drilling rate increased by 25.51%, achieving obvious results. Due to the reasonable selection of special nozzles, the drill bit has the highest specific water power and the mechanical drilling speed is significantly increased. 2.1.5 Bottomhole pressure difference Bottomhole pressure difference is the main factor restricting the drilling speed of roller cone bits. If conditions permit, reduce the pressure difference as much as possible to achieve balance or * * Balanced pressure drilling. In view of the low formation pressure coefficient (only 0.6-0.8) in the old oil area of Qinghai Oilfield, an oil-in-water emulsion drilling fluid system was used in the Huatugou block. The density of the drilling fluid was controlled at 0.95-1.05g/cm3, and the oil content was controlled at 20%-30%. This reduced the holding effect of bottom hole cuttings, significantly increased the drilling speed, and effectively solved the problem of oil and gas layer pollution. The average crude oil production of a single well also increased significantly. 2.2 Anti-deviation and straightening technology Anti-deviation and straightening technology is one of the key technologies for small displacement wells. The adjustment well completed in 2001 is located in a block where the stratigraphic inclination angle changes greatly, and there is a common problem of difficulty in controlling the well deviation. If the deviation is not prevented during drilling, the well deviation will be large and the deviation will be corrected by hoisting, or even the quality of the well body such as filling sidetracking does not meet the design requirements, which will seriously affect the drilling speed and economic benefits. There are many reasons for well deviation, including formation factors, equipment installation factors, drilling tool structure and drilling technical measures, etc. Formation factors are the main cause of well deviation. Therefore, we have worked hard on management and formulated practical technical measures to prevent deviation and straightening, including strictly controlling the quality of equipment installation, optimizing drilling tool assemblies, optimizing drilling parameters, and measuring inclination at fixed points to track wellbore trajectories in a timely manner. This has minimized the factors causing man-made deviations. At the same time, we have selected reasonable torsional azimuth points and timely installed wired kickbacks while drilling for wells whose predicted displacement or trajectory exceeds the standard. Of the 22 wells completed in 2001, not a single well was hoisted due to excessive well deviation or filled with sidetracking due to substandard well quality. The well quality pass rate is 100%, and the high-quality rate is 78%, which effectively solves the problem of large well deviation affecting the mechanical penetration rate during drilling and thus affecting economic benefits. 2.3 Cluster well borehole trajectory anti-collision technology In 2001, 31 wells were deployed in Huatugou Oilfield, of which 9 wells were directional wells. Due to the undulating mountains on the surface of the oil field, the workload of earthwork before drilling is very large, and the well site is often too small to even place the drilling tools. Five of the nine wells are old wells, and the distance between the wellheads is less than 10m. Cluster directional wellbore anti-collision technology has become the primary task of this type of wells. The measures we take for this type of wells are:: (1) Investigate the drilling data of adjacent wells and prepare a well trajectory map and a well trajectory anti-collision map ； (2) Find the point or well section with the highest probability of collision and give special reminders. If it is found that the probability of collision in the vertical well section is high, request Party A to change the designed deflection point to avoid the possible collision section. ； (3) Reserve sufficient margin for some too old wells when making wellbore trajectory anti-collision maps ； (4) Application of wired measuring-while-drilling instruments to create angles ； (5) Closely observe the impact of ferrous materials on the wired while-drilling instrument when drilling and tilting. It is found that the magnetic field strength is greater than the normal value and the azimuth value is unstable due to abnormal effects. Stop drilling immediately to determine and analyze the source and direction of the ferrous material in order to take measures to avoid obstacles. ； (6) If there is a high probability of collision with adjacent wells in the stably inclined well section, intensify the inclination measurement, adjust the well inclination and orientation in a timely manner while drilling, and safely bypass the obstacle. 2.4 Composite leakage prevention and plugging technology In drilling wells in Huatugou, Shizigou, Qiquan and other blocks, well leakage often occurs. For example, in the S4-2 well constructed in 1999, the leakage loss was as high as 1838m3, which seriously restricted the drilling progress, prolonged the drilling cycle, and caused a large amount of economic losses. The comparison between well leakage in 2001 and 2000 is shown in Table 1. It can be seen from the data in Table 1 that the number of leaks and the amount of leaks in 2001 were lower than in 2000. Mainly in view of the characteristics of the upper stratum with developed holes and structural fractures, loose structure, high permeability, easy formation of leakage channels, fast leakage speed, large leakage amount, relatively concentrated well sections, and the middle and lower parts that are prone to leakage mainly due to faults or broken formations, the composite leakage prevention and plugging technology has been implemented to effectively control the occurrence of well leakage. 2.5 Solid control equipment application technology Good drilling fluid performance must be guaranteed by good solid control equipment. Our company is not only equipped with desanders and centrifuges for each well team, but also formulates strict usage, maintenance and upkeep measures. The application technology of solid control equipment, mainly high-mesh vibrating screens, desanders and centrifuges, effectively ensures the maintenance of drilling fluid performance, ensures underground safety, and lays a good foundation for rapid drilling. 2.6 Acid-soaking process to remove stuck. Large sections of gray mudstone and gray silty mudstone are common in the formations drilled in the Qinghai Oilfield. They have high CaCO3 content and are strongly dispersed and highly expanded formations. There are three main types of drill stuck accidents that are prone to occur during drilling.: Pressure differential stuck (such as the drilling fluid density in the Nanbaxian area is as high as 2.18g/cm3 and is easy to stick), reduced diameter stuck (such as the S3-3-2 well in the Huatugou area) and well wall collapse and embedded stuck (such as the S32 Incline 1 well constructed in 1998). In the past, the main measures taken to deal with drill stuck accidents were:: The jar shocks to release jamming, the jamming agent is soaked to release jamming, and the sleeve milling is reversed to release jamming. However, these measures have certain limitations. The soaking effect of the jam release agent is poor, the jam release rate is low, and the tool jam release time is long and the cost is high. In view of the high CaCO3 content in the formation of Qinghai Oilfield, through many indoor experiments, we chose the measure of soaking in hydrochloric acid to remove stuck. The construction steps are: ①A 5m3 homemade acid storage tank is connected to the drilling pump, and the hydrochloric acid is diluted with water to a concentration of 15%. ； ②ground floor jar ； ③First, add 2m3 of clean water as the pre-isolation fluid, pump in 3m3 of 15% hydrochloric acid, and then add 2m3 of clean water as the post-isolation fluid. ； ④Calculate the annulus volume inside the drilling tool and under the stuck point to determine the amount of slurry replacement ； ⑤Use drilling fluid to displace hydrochloric acid out of the drilling tool to the stuck point, stop the pump, increase the frequency of moving the drilling tool, shock, and pump up ； ⑥After the jam is released, the acid solution is immediately replaced, and the drilling tool is continuously moved according to the specific conditions downhole. ； ⑦ÑTreat the drilling fluid around the hole. 3. Cementing Technology Due to the low formation pressure coefficient (0.6-0.8), the cement slurry is required to return to the surface, resulting in serious cement slurry leakage, ranging from tens of cubic meters to hundreds of cubic meters. Conventional cementing methods are prone to leakage, resulting in low return of cement slurry, leakage of sealing of oil and gas layers, or failure of sealing, resulting in failure of production layers, etc. Through a large number of indoor experiments, we guided the actual cementing construction according to the formation characteristics and previous sound amplitudes, improved the cement slurry formula, and researched and summarized the cementing technology using a two-base and two-condensing cement slurry system. Two-base and two-condensation means that conventional cement slurry accelerating setting agent is used in the lower main oil layer section, and bubble cement slurry plus retarder is used in the upper leakage-prone layer section. The dividing point is reasonably selected based on the electrical measurement results, formation pressure distribution, and oil and gas layer distribution. After on-site application, the problems that occurred in the previous cementing construction were basically solved. 4. Drilling fluid technology 4.1 Oil-in-water emulsified drilling fluid technology The geological conditions of Huatugou Oilfield are complex, with low formation pressure coefficient, loose shallow strata, developed faults and fractures, shallow, numerous, thin and scattered oil and gas layers, and serious leakage during drilling. By using oil-in-water emulsion drilling fluid technology in 12 wells in this block and for the first time in Qinghai Oilfield, the drilling fluid density was reduced from the original 1.10~1.20g/cm3 to 0.95~1.05g/cm3, and the oil saturation of the drilling fluid was controlled at 20%~30%, successfully solving the problems of lost circulation and low production. At the same time, the mechanical drilling rate is maximized, the drilling and completion cycle is shortened, and the soaking time of drilling fluid and completion fluid in the oil and gas layer is shortened, thereby achieving the purpose of protecting the oil and gas layer and improving recovery rate. Oil-in-water emulsion drilling fluid has been successfully used in 12 wells in Huatugou Oilfield. 4.2 Strong Inhibitory Drilling Fluid Technology The middle and lower strata in the Huatugou, Shizigou, Qiquan and other blocks are all highly dispersed and strong expansion formations. The mudstone section absorbs water and expands, and the wellbore shrinks, resulting in difficulty in drilling, frequent drilling and back drilling, resistance to electrical testing, and even accidents such as drill stuck. The positively charged gel drilling fluid and KCl polymer drilling fluid that have been used in the past have certain shortcomings. Positive electrogel drilling fluid has strict requirements on the solid phase and bentonite content in the drilling fluid. The viscosity is relatively high, and the water loss is controlled at 7 to 12 mL, which is difficult to further reduce. KCl polymer drilling fluid increases the density of the drilling fluid, and its use is limited in areas that require lower drilling fluid density. For this purpose, a highly inhibitory zwitterionic polymer drilling fluid was selected to overcome the limitations of the above two systems, meet the requirements of inhibiting the hydration expansion of the mudstone formation and dispersing pulping, and achieve the purpose of reducing diameter shrinkage, preventing collapse, and preventing jamming. The specific formula is: 0.3%～0.5% FA-367+0.2%～0.3% HT-201+ (0.5%～1%) NH4HPAN (SD-17W) + (1%～2%) LFT-70. 5. Oil and gas layer protection technology: Based on the type and characteristics of the reservoir, the following oil and gas layer protection measures are taken: (1) Use high-quality polymer drilling fluid and apply high-pressure jet drilling technology to increase drilling speed and reduce the soaking time of oil and gas layers. (2) Reduce density as much as possible to achieve * * For balanced pressure drilling, for example, 12 wells in Huatugou Oilfield use oil-in-water drilling fluid, with the density controlled at 0.95~1.05g/cm3. (3) Select a highly inhibitory drilling fluid system to control water loss within 5 mL to reduce the damage to oil and gas layers caused by hydration, dispersion and water absorption expansion of shale. (4) Vibrating screens, desanders, centrifuges and other purification equipment should be used on site. The mesh size of the vibrating screens should reach 80 to 100 meshes, and the use time should be 100% of the total ring time to reduce and eliminate harmful solid phases in the drilling fluid and minimize the damage to the oil and gas layers caused by harmful solid phases. (5) Use shielding temporary plugging agents (QS, DUP-2, LFT-70) in drilling fluids to improve wall-building properties and prevent permeability leakage in sandstone and micro-fracture reservoirs and the invasion of harmful solid phases in the drilling fluid. (6) Choose a lower pH value to avoid serious damage to oil and gas layers caused by the reaction of high-concentration OH- with Ca2+ and Mg2+ in the formation to form Ca(OH)2 and Mg(OH)2 precipitates. (7) Maintain the amount of inhibitor added to stabilize the well wall and reduce downhole complications. Update equipment in a timely manner, strengthen production organization, reduce non-production time such as repairs and organization shutdowns, and shorten the drilling cycle. (8) Strictly control the drilling fluid performance, especially the fluid loss must be controlled within 5 mL to reduce damage to the oil and gas layers caused by excessive drilling fluid fluid loss intruding into the formation. By implementing the above oil and gas layer protection technologies, the damage to the drilled oil and gas layers has been greatly reduced, and the daily production in the same block and the same layer has been significantly increased. 6. Understanding and suggestions (1) In view of the complex conditions of adjustment wells in Huatugou, Shizigou and other oil fields in Qinghai, the comprehensive supporting technology for adjustment well drilling has been developed through exploration, practice, and summary. It has strong practicability and reliability, has been fully verified in drilling practice, and is easy to implement and promote. (2) Through the implementation of 22 wells, complex problems such as leakage, well collapse, diameter reduction, delayed drilling and easy loss of cement slurry during well completion and cementing in the area have been better solved. The average mechanical drilling speed of the adjusted wells has reached 17.24m/h, and significant economic and social benefits have been achieved. (3) Drilling engineering is a systematic engineering that integrates technology, equipment, management, etc. Therefore, all links in the entire drilling process should cooperate and support each other, so as to achieve better results.